Is using a quad instead of triangles to represent an equivalent area, say the elongated part of the model above, improve computation efficiency?
hlin1
A quad can be represented with two triangles. If triangles are stored as points, a quad would save 2/6 points or 33% memory. A quick search of Wikipedia shows that quad meshes are commonly used. I wonder why shapes with more edges aren't used.
ceviri
If you use shapes with more edges you lose the guarantee that the face will be planar, so there might be annoyances in that end.
Azure
Also every set of 3 points uniquely define a triangle, but if you have more points, there are multiple polygons that can fit those points.
dtorresr
Yea I feel that if you save space from storing "less points", you still need some overhead to store how the points in these complex polygons are connected. Or maybe the edges are decided based on the order in which the points are stored. Plus I wonder how annoying it would be to keep them on the same plane.
Arthas007
@Azure, well if the points are all vertexes, there is only one possible polygon(refer to the convex-hull theory)
keenan
There are a lot of trade offs between triangle and quad meshes. The most significant one, perhaps, is that generating pure quad meshes (i.e., all quads; no triangles or other polygons) takes some rather sophisticated algorithms, whereas generating triangulated surfaces is much easier. Also, as mentioned by @Azure, three points always make a triangle, whereas four points do not in general make a planar quad. (@Arthas007: note that if four points don't share a plane then their convex hull won't be a quadrilateral---it will be a tetrahedron!). On the other hand, quads have some appealing features---for instance, every point on a smooth surface has two orthogonal directions of "principal curvature," i.e., directions where the surface bends most/least, and meshes roughly aligned with these directions give very good approximation of not only the surface but also quantities like normals, etc. Perhaps for this reason, artists often claim that quad meshes provide more natural degrees of freedom for modeling organic shapes like faces, bodies, etc. Nice survey discussing quad meshing here.
Is using a quad instead of triangles to represent an equivalent area, say the elongated part of the model above, improve computation efficiency?
A quad can be represented with two triangles. If triangles are stored as points, a quad would save 2/6 points or 33% memory. A quick search of Wikipedia shows that quad meshes are commonly used. I wonder why shapes with more edges aren't used.
If you use shapes with more edges you lose the guarantee that the face will be planar, so there might be annoyances in that end.
Also every set of 3 points uniquely define a triangle, but if you have more points, there are multiple polygons that can fit those points.
Yea I feel that if you save space from storing "less points", you still need some overhead to store how the points in these complex polygons are connected. Or maybe the edges are decided based on the order in which the points are stored. Plus I wonder how annoying it would be to keep them on the same plane.
@Azure, well if the points are all vertexes, there is only one possible polygon(refer to the convex-hull theory)
There are a lot of trade offs between triangle and quad meshes. The most significant one, perhaps, is that generating pure quad meshes (i.e., all quads; no triangles or other polygons) takes some rather sophisticated algorithms, whereas generating triangulated surfaces is much easier. Also, as mentioned by @Azure, three points always make a triangle, whereas four points do not in general make a planar quad. (@Arthas007: note that if four points don't share a plane then their convex hull won't be a quadrilateral---it will be a tetrahedron!). On the other hand, quads have some appealing features---for instance, every point on a smooth surface has two orthogonal directions of "principal curvature," i.e., directions where the surface bends most/least, and meshes roughly aligned with these directions give very good approximation of not only the surface but also quantities like normals, etc. Perhaps for this reason, artists often claim that quad meshes provide more natural degrees of freedom for modeling organic shapes like faces, bodies, etc. Nice survey discussing quad meshing here.